1. Field of the Invention
The present invention relates to an optical fiber-fixing substrate having a fixing groove for receiving and fixing an optical fiber therein, and a method of producing the same.
2. Description of Related Art
Various substrates are known for fixing an optical fiber having a diameter of, for example, around 125 .mu.m. In any type of substrate, a light beam transmission loss between the optical fiber and another light beam transmitting means becomes large, if the axis of the optical fiber is displaced from a desired position. Thus, working of a very high precision of the fixing groove, such as not over than 0.5 .mu.m, is required for fixing the optical fiber. FIG. 1(a) is a perspective view of an example of such a substrate, wherein a main body 2 of a substrate 34 for fixing an optical fiber is made of a glass or ceramics. A plural number of so-called V grooves 12 extend in the upper surface of the substrate main body 2 from an end towards the opposing end of the upper surface. The grooves 12 are formed parallel to each other. In the V groove 12, an inclined surface 7 extends substantially linearly between the ridge 43 and the bottom 11. Thus, the V grooves 12 have a V shaped cross-section. The respective V groove 12 is minute having a depth of around a hundred and several tens .mu.m, for example.
In producing such a substrate for fixing an optical fiber, the V grooves may be formed by a method of etching a silicon material. However, the method has a limit in the working precision and could hardly produce the V grooves of a high precision of more than a certain extent. Thus, in order to accomplish such a high precision, a method of forming the V grooves has been used wherein, alumina, agate, zirconia or the like ceramics is worked by grinding. In such a case, the V grooves are formed by, for example, sintering a shaped ceramic body to prepare a sintered body, plane grinding the sintered body to prepare a flat surface, and then grinding the flat surface by a diamond grinding wheel. At that time, when the grinding is effected by a diamond grinding wheel, the grinding is effected in a constant direction, so that each V groove 12 extends respectively linearly and parallel to each other from an end towards the opposing end of the flat surface of the main body 2, as shown in FIG. 1(a).
The substrate 34 having the optical fibers 9 received and fixed in the respective V groove 12 has to be optically coupled to other light beam transmitting devices. Namely, if an optical fiber is used as another light beam transmitting device, a separate optical fiber is prepared, the end surface of the optical fiber fixed in the V groove 12 is contacted with the end surface of the separate optical fiber, and the contacted portions of the optical fibers are heated and melted to connect the optical fibers. Thereafter, the connected optical fibers are removed from the respective fixing groove.
As an alternative example, if an optical guide wave is used as another light beam transmitting device, an optical waveguide substrate having provided an optical waveguide is prepared. Each optical fiber 9 is fixed in the respective V groove 12, and an adhesive agent layer 8 is formed around the optical fibers 9 to firmly join each optical fiber 9 to the main body 2 of the substrate 34. A lid 32 is joined onto the substrate 34 to prepare an assembly as shown in FIG. 1(b). Thereafter, the end surface 33 of the substrate 34 is polished by grinding and the end surface of the optical waveguide is polished by grinding to a high precision, the polished end surfaces of the two substrates are joined to each other, and the other end surface of the respective optical waveguide is optically coupled to the end surface of the corresponding respective optical fiber.
The substrate 34 is applicable also to a core wire selecting device as described in I. Nakanishi et al "Study of an Optical Fiber Movable Type Core Wire Selecting Device" reported in Electro Information Communication Society, Communication Society General Meeting B-651, 1995. In this case, an optical fiber is fixed until the middle of the V groove, and the end surface of the optical fiber is optically polished. A master optical fiber is received in the V groove to oppose the optically polished end surface of the already fixed optical fiber. In such a state, light beams can be passed and guided from the master optical fiber to the respective optical fiber. By this means, experiments can be performed, such as, detection of trouble of the optical core wire.
The inventors have found out the following problem in the process of studying the form of such an optical fiber-fixing substrate. Namely, when the respective optical fiber 9 is received in the respective V groove 12 of the substrate 34 as shown in FIG. 1(a) and the surface of the substrate 34 is carefully observed by a survey type electron microscope, a minute defect or fragmented portion 30 is found sometimes at a portion of the top 10 of the ridge 43 or a portion 10A of the flat surface as exaggeratedly shown in FIG. 1(a). Such a defect 30 is likely formed when the optical fibers 9 is received in the respective V groove 12. Formation of the defect 30 may have an adverse influence over the optical fiber 9, so that the substrate 34 having the defect 30 has to be discarded as a rejected part resulting in the increase in production costs.
Particularly, in case when the optical fiber is coupled to an optical waveguide, the end surface 33 of the substrate 34 of the assembly shown in FIG. 1(b) has to be polished by grinding as described above. However, subsequent study of the polished surface revealed sometimes a minute defect 31 at the edge of the ridge 10 or 10A. Such a defect also should not be formed, because a situation is considered that the precision of the coupled portion of the end surface of the optical waveguide and the end surface of the substrate 34 is decreased by the fragment 35 produced by the defect when coupling the both end surface to each other, or a situation is considered that deterioration of the substrate 34 proceeds from the defect 30 when the coupled article of the optical waveguide and the substrate 34 is used in a strict environmental condition for a long period of time.
In addition, in the aforedescribed optical fiber movable type core wire selecting device, the master optical fiber is inserted in the inlet or opening of the respective V groove and moved in the respective V groove towards the respective optical fiber. However, the respective master optical fiber is likely damaged when the respective master optical fiber is collided against the respective ridge at the neighborhood of the opening of the V groove. Such a damage of the master optical fiber is a problem because the inspection of the trouble of the optical core wires can not be performed.